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Project Scope

A major city in Florida had been experiencing chronic hydrogen sulfide (H2S) odor and corrosion problems at a forcemain discharge manhole and further downstream at a lift station, resulting in community complaints and collection system corrosion. Furthermore, the forcemain was located in the median of a busy roadway with no place to store a permanent chemical injection system. USP Technologies (USP) performed a system trial utilizing Cloevis Biofilm Removal Service. The trial quickly reduced H2S to desired levels at both control points and eliminated all odor complaints.

Technology

Cloevis Biofilm Removal Service (Cloevis BRS) is an innovative technology offering that removes the biofilms that adhere to the inner surfaces of wastewater forcemain walls, including the underlying Sulfate Reducing Bacteria (SRB) that produce hydrogen sulfide. As a result, gaseous hydrogen sulfide (H2S) production is eliminated. The treatment requires an initial conditioning period when the biofilm that harbors the SRB’s is removed, followed by maintenance treatments that are repeated as monitored lines show signs of SRB reformation.

Control of H2S has been achieved in wastewater collection systems with the utilization of many different technologies such as oxidation, precipitation, pH adjustments and vapor-phase systems. Cloevis BRS offers the benefits of lower cost, avoidance or minimization of on-site chemical storage, is unaffected by sulfide loading, retention time or oxygen uptake and has no labor/ maintenance demand. Other benefits include complete removal of sulfide odors for up to three weeks after treatment cycle and elimination of methane production within the treated segment as well as no downstream adverse impacts due to residual treatment chemicals. In addition, the effective cost of Cloevis BRS is similar to caustic shocking and less than conventional continuous chemical feed alternatives such as nitrate and iron salts.

Solution

The City’s forcemain length is 8,600 feet with a diameter of 8-10 inches and a retention time of 4-6 hours. It has a wastewater flow of 0.128 MGD, and prior to Cloevis BRS treatment, had baseline H2S vapor levels at 50-119 ppm and total liquid sulfide levels at 7.8 mg/L at the control location.

The initial conditioning period involved two separate 24-hour treatments which were completed two days apart. Maintenance treatments included one 12-hour treatment after the first 12 days and one 8-hour treatment after an additional 24 days. Ongoing maintenance Cloevis BRS treatments are completed every 3-4 weeks, depending on the rate of biofilm regeneration. Since the initial conditioning period, H2S average levels have steadily been at 5 PPM or less at the forcemain discharge manhole and sulfides at the downstream lift station have been greatly reduced. Additionally, odor complaints have ceased at these locations since USP began Cloevis BRS treatment.

Read More Download Sulfide Control with Cloevis Biofilm Removal Service (pdf)[/vc_column_text][/vc_column][/vc_row]

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Project Scope

A field demonstration was initiated in February 2014 by the Suffolk County Department of Public Works (SCDPW) to quantify the impacts of Peroxide Regenerated Iron-Technology (PRI-TECH®) as a more economic approach in maintaining odor control in the solids handling phase at the Bergen Point Wastewater Treatment Plant (WWTP).

For approximately the last 30 years, the SCDPW Bergen Point WWTP has treated H2S and reduced sulfur compound-based odors in the sludge handling phase at the facility with potassium permanganate (KMnO4). The sludge handling phase includes unstabilized sludge waste from three locations: sludge from the primary clarifiers; thickened waste activated sludge; and chemical sludge from the facility’s scavenger sludge collection system. The three streams are co-mingled in a 0.25 million gallon capacity sludge blend tank (SBT) that is turned over approximately every 24 hours. The blended sludge is then pumped from the SBT to belt filter presses where it is dewatered and sent via screw conveyor to trailers located outside of the solids handling building. Unstabilized sludge has many more odor causing compounds versus digested sludge so the program needed to be capable of treating odors at all stages of the solids handling operation up to and including the off-site disposal facilities.

Suffolk County explored a PRI-TECH® demonstration program in an effort to achieve equal or better performance than the historical potassium permanganate odor control program while reducing operating costs. This demonstration evaluated the use of PRI-TECH® for controlling sludge odors, composed mainly of hydrogen sulfide gas and reduced sulfur compounds (mercaptans, etc.), while maintaining the belt filter press operation.

Technology

PRI-TECH® is a proprietary odor control technology that utilizes iron salts and oxidants in a fashion that reduces sulfides to elementary sulfur and reduces sulfur compounds to non-odorous compounds. This program was implemented by adding ferrous chloride (FeCl2) as the primary sulfide control agent into the primary sludge line upstream of the sludge blend tank. Hydrogen peroxide (H2O2) was added downstream at the sludge blend tank recirculation pumps to regenerate iron from ferrous sulfide (FeS) to either free ferrous and/or ferric iron. The H2O2 was also added to the online belt press feed pumps discharge piping to provide additional iron regeneration, oxidation of odorants and durational odor control. The iron also acts as a catalyst to allow the hydrogen peroxide to quickly and efficiently oxidize reduced sulfur compounds.

Solution

Odor control performance was analyzed by measuring liquid sulfide and mercaptan levels through a “shake” test in which these compounds are stripped into the vapor phase and analyzed with either OdaLog® portable gaseous hydrogen sulfide (H2S) instruments or H2S and RSH colorimetric tubes. In addition, H2S was measured continuously in the headspace of the SBT with an OdaLog® vapor H2S datalogger that had cellular transmission capability to allow for collecting data without disturbing the instrument and to allow for alarm set points to be established. Qualitative and quantitative monitoring of the dewatered biosolids trailer staging area was also performed. After program optimization during the demonstration period and ongoing operation, there were little to no recorded sulfides or mercaptans in the treated sludge from the SBT via shake test analysis. H2S levels were statistically similar in the SBT headspace averaging 0.2 ppm with a peak of 9 ppm under PRI-TECH® operation versus an average of 0.2 ppm with a peak of 14 ppm under the prior year’s KMnO4 operation.

The program monitoring was expanded beyond the plant to the outside disposal sites. Analytical methods for evaluating specific odor compounds were not available at any of the disposal sites. Durational odor control was evaluated based on subjective experiences and qualitative feedback of the operators at the disposal sites. According to operators, optimization of the program, which included the use of targeted dosing profiles, produced a reduction in odors at the disposal sites.

An additional benefit of the PRI-TECH® program is the potential to generate ferric iron (Fe3+) coagulant when the proper amount of H2O2 is added, which could assist in sludge dewatering and in producing higher percent solids in the pressed filter cake. Ferric iron is generated through the reaction of ferrous iron and hydrogen peroxide. During the demonstration period and ongoing operation over the first year, polymer use rates were unaffected and an increase in percent solids was noted in the filter cake from a comparable period the previous year.

Read More Biosolids Odor Control via Peroxide Regenerated Iron –PRI-TECH® Technology[/vc_column_text][/vc_column][/vc_row]

Project Scope

A Midwest wastewater treatment plant was struggling with problematic hydrogen sulfide (H₂S) levels at two points within their facility arising from biosolids processing. The factors driving the need for H₂S control included worker safety, corrosion of electronics and concrete, implied regulatory limits and odor control. Along with normal residential and commercial flows, the facility also receives unpredictable slugs of high biological oxygen demand (BOD) wastewater from agricultural industries and handles septage hauler loads from a wide radius. USP Technologies (USP) implemented a full-service hydrogen peroxide (H₂O₂) solution with operator-adjustable dosing options to account for the unpredictable sulfide loadings and to lower H₂S to acceptable levels at both their biosolids holding tank and dewatering building.

Technology

H₂O₂ is ideally suited to remove H₂S from wastewater solids, provided that sufficient contact times are available – typically 2-5 minutes prior to the dewatering device. The efficiency of treatment depends upon the available reaction time, the initial level of H₂S and the relevance of non-H₂S odors. Under optimal conditions, effective dose ratios are about 5 parts H₂O₂ per part aqueous sulfide, and can be reliably estimated through beaker tests. The chemical reaction is as follows:

H₂S + H₂O₂ → S0 + 2H₂O

Background

A biosolids holding tank receives all biosolids awaiting dewatering at the plant’s two belt filter presses. The tank is generally emptied every one to three days depending on biosolids generation rates correlated with industrial discharge volumes. The biosolids entering the tank, especially from the gravity thickeners, contain a significant sulfide load throughout the entire year. The holding tank employs mechanical mixing and aeration to minimize further sulfide generation, however, this causes extreme volatilization of H₂S, exceeding 500 ppm. Previous control methods, including iron salt addition and “in-situ scrubbing” using a hydroxyl ion generating system only provided limited success in achieving desired targets.

Compounding the challenge, the radicals generated interfered with the proper measurement of H₂S. From the holding tank, biosolids are pumped to a dewatering building housing two belt filter presses. The turbulence of these belt filter presses causes most of the sulfide present to volatilize. A wet scrubber was installed and used for years to control the H₂S, however, by 2014 it was at the end of its serviceable lifespan.

Solution

USP was invited to visit the facility to determine a more effective treatment strategy. Bench scale dose response tests utilizing shake tests were then conducted to determine theoretical hydrogen peroxide dosing needs and possible reaction times from several injection points. The optimal injection point was determined to be at the biosolids pump outlet, which provided approximately 3 minutes of reaction time before reaching the belt filter presses.

Shortly afterwards, a full-scale H₂O₂ storage and dosing equipment system was installed. The H₂O₂ pumps were connected by relays to the biosolids pumps to ensure that H₂O₂ only dosed while the biosolids pumps were running. The program was demonstrated to be effective within the first hour of operation, with H₂S levels brought down below 1 PPM both above the belt filter presses and within the dewatering building’s main room. The program continued with dosing rates throughout the first six months ranging from 1.5 to 6 gallons/hour.

In addition, the operators were trained on how to both raise and lower dosing rates based on the observed H₂S levels to mitigate variable industrial loadings. The removal of H₂S from the dewatering facility eliminated the need for a costly replacement of their wet scrubber, and the customer invited USP to co-present our success story at their state conference.

Read More Biosolids Odor Control at Holding Tank and Belt Filter Presses via Hydrogen Peroxide[/vc_column_text][/vc_column][/vc_row]